In order to increase the sharpness of an image of an object, a contour-emphasizing apparatus is generally built in a television camera. In this contour-emphasizing apparatus, as shown in FIG. 5A, an image signal [a luminance signal in case of a black-and-white television and a signal of three elementary colors (a signal formed by mixing signals R, G and B) in case of a color television] is differentiated to extract a contour signal as shown in FIG. 5B, and this contour signal is added to the original image signal [an R(red) signal., a G(green) signal and a B(blue) signal in case of a color television] to obtain a contour-emphasized image signal as shown in FIG. 5C.
In this conventional contour-emphasizing process, since the level of the contour signal is determined, as pointed out above, by the differential value of the level of the image signal, that is, the difference of the level between both the sides of the contour, not only in the bright region where the level of the image signal is high but also in the dark region where the level of the image signal is low, the level of the contour signal is the same if the difference of the level between both the sides of the contour is the same, and therefore, the contour-emphasizing degree is the same.
However, it is known that the visual resolving power of a man in the dark region is less than that in the bright region, and the contour-discriminating capacity in the dark region is poorer. Therefore, according to the above-mentioned contour-emphasizing process, the contour of the dark region is obscure and the image is illegible.
If the level of the contour-emphasizing signal is indiscriminately increased so as to clarify the contour of the dark region, the contour of the bright region is excessively emphasized and an image having striking streaks in the bright region is formed and also this image is illegible.
The present invention has been completed under this background, and it is a primary object of the present invention to provide a contour-emphasizing apparatus in a television camera, in which by correcting the level of an image signal before the emphasis of the contour, the contour is appropriately emphasized not only in the dark region but also in the bright region to increase the image quality.